Japanese Knotweed

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Japanese Knotweed

There has been recent publicity concerning the proposed release of Aphalara itadori, which feeds exclusively (or virtually so) on Japanese knotweed. A considerable amount of research has been undertaken, which may be summarized as: it only feeds on Japanese knotweed and when the population levels are high enough will weaken the knotweed plants and reduce their vigor by sucking the sap. Hopefully this will also reduce the spread of the knotweed into new areas. Additionally the psyllids were not able to successfully reproduce on any other tested species.

So why should Wreford as knotweed contractors support this initiative? Well most Japanese knotweed infestations are never treated. In fact there is far more knotweed growing in this country than is ever treated. I personally have visited several sites over the years, where the knotweed covers hectares in large stands and is still not being treated. I have also visited several towns and communities, where knotweed is covering over 25% of the available land area and little or no control measures are (apparently) in place. This would be the future for all of us, unless new legislation is passed forcing all landowners to treat invasive weeds on their land or biological control is introduced. Who would pay for the chemical control of knotweed? It would run into hundreds of millions of pounds every year for years, perhaps decades.

Obviously there are risks to biological agents being released. The main risks that are cited are that we don't know what will or will not happen. Once released, that will be that. If it all goes wrong, there may not be a realistic prospect of exterminating the released psyllids. The human species has only ever exterminated one pest insect - the Rocky Mountain Locust - and that was an accident! We also know that related species of Psyllid have the ability to travel (although it is a weak flyer, it migrates using wind currents) hundreds of miles in one year, so it is probable that the insect will naturally travel over the English Channel into France, Germany, etc, where they have a similar knotweed problem. While I am confident that the research done to date is good, it has focused on the British Isles. How far will the psyllids spread? What will be the impact on native species in mainland Europe? These are questions that need addressing and to date (to my knowledge) have not been adequately answered.

As a contractor and conservation volunteer, I understand that we need biological control to have any chance of maintaining our countries biodiversity against rapidly spreading invasive weeds, but before we release another species into our ecosystem, we need to understand that we are not isolated geographically and whether our introduction of new species will or will not impact upon other countries biodiversities. We need to ensure that we are not causing long term problems to our neighbors or to ourselves. I would ask that we establish how far the psyllids are likely to spread and what the risks (if any) to native flora within this range are.

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Japanese Knotweed